1. Field of the Invention
The present invention relates to a surface treatment method and apparatus using plasma, and more particularly to a surface treatment method and apparatus for forming a film or modifying a surface in a multilayer structure device such as a semiconductor device and a liquid crystal device, and for forming a film of various functional materials or modifying a surface, using high-pressure plasma at high speed and under clean atmosphere. The word xe2x80x9csurface treatmentxe2x80x9d generically includes the above-described film formation and surface modification.
2. Description of the Related Art
Plasma CVD is known as a method for forming a film in a multilayer structure of various devices such as a semiconductor device and a liquid crystal device or a film of various functional materials. The plasma CVD is now widely used in actual manufacturing processes. Plasma is also used in a known method for modifying a surface.
In the above-described plasma CVD or plasma surface modification method, reactive gas is selected in accordance with target film formation or surface modification. A high electric field is applied to the selected gas to be in a plasma state. Using active seeds generated in the plasma, a film is formed on a target surface or a target surface is modified. There are various techniques of generating plasma. In these techniques, plasma generation may be performed in various ranges of pressure and the like. The range of the applied preesure is not clearly defined. When plasma generation is performed under a low pressure, the density of the active seeds is low, so that the rate of film formation or surface modification is slow. For this reason, the throughput of an apparatus is small, contributing to an increase in cost of the product.
To solve the above-described problems and improve the rate of film formation or surface modification, the plasma generation may be performed under a high pressure which is as high as atmospheric pressure so that the density of the active seeds is increased. This method is, for example, disclosed by Japanese Laid-Open Publication Nos. 2-50969, 2-73978, or 2-73979. Hereinafter, a method disclosed by Japanese Laid-Open Publication No. 2-73978 will be described with reference to FIG. 24.
FIG. 24 is a diagram illustrating a configuration of an apparatus disclosed in the above-described publication. In FIG. 24, the apparatus includes a film formation chamber 241, a non-ground electrode 242, a ground electrode 243, a porous plate high resistor 244, a sample substrate 245, a gas inlet 246, a RF power supply 247, a heater 248, and a gas outlet 249.
According to the above-described publication, the electrodes 242 and 243 are arranged to face each other in the film formation chamber 241. The RF power supply 247 is connected to the non-ground electrode 242. The ground electrode 243 is connected to the ground. A high resistor (not shown), which has a size greater than or equal to the ground electrode 243, is optionally provided on the ground electrode 243. The sample substrate 245 is provided on the high resistor. The porous plate high resistor 244 is attached to the non-ground electrode 242. A gas mixture of a gas for film formation and He gas is supplied into the film formation chamber 241 from the inside of the non-ground electrode 242 through the holes of the porous plate high resistor 244. The supplied gas is simultaneously discharged from the gas outlet 249 so that the inside of the film formation chamber 241 keeps a pressure around the atmospheric pressure. In this case, when a distance between the porous plate high resistor 244 and the sample substrate 245 is defined as a intersubstrate gap 240g, the intersubstrate gap 240g is between or equal to 0.1 mm and 10 mm.
In the above-described structure, radio frequency power is supplied to the non-ground electrode 242 from the RP power supply 247. Atmospheric pressure plasma 240p is generated between the non-ground electrode 242 and the ground electrode 243 so that the film formation is performed on the sample substrate 245.
Experiments on the film formation were conducted using the conventional apparatus shown in FIG. 24. The conditions of the experiments are shown below in Table 1. The results of the experiments are shown below in Tables 2 and 3. Table 2 indicates a correlation between the intersubstrate gap 240g and a film thickness distribution. Table 3 indicates a correlation between a value Q/S and a film formation rate in the central portion of the substrate 245, where the value Q/S is obtained by dividing an overall gas flow amount Q by the plasma volume S.
As is seen from Tables 1 through 3, the apparatus disclosed in the above-described publication has the following features:
(1) the material gas for the film formation is diluted with a large amount of He gas for the purpose of obtaining a stable glow discharge;
(2) to form a uniform film over a large area, the high resistor 244 is provided on at least one of the electrodes 242 and 243. For this reason, a direct current does not flow, but only an alternating current flows. A current density per unit area is thus restricted, so that the plasma 240p can be uniformly spread:
(3) according to the experiment results shown in Table 2, the smaller the gap 240g between the sample substrate 245 and the high resistor 244, the smaller and more uniform the film thickness distribution of the obtained film. For this reason, the gap 240g between the sample substrate 245 and the high resistor 244 is set to 10 mm to 0.1 mm: and
(4) according to the experiment results shown in Table 3, when the value Q/S which is obtained by dividing the overall gas flow amount Q by the discharge space volume S is 10xe2x88x921 secxe2x88x921, the supplied material gas is quickly decomposed. The film formation rate on the substrate 245 is decreased. On the other hand, when the value Q/S is large, the supply gas passes through the plasma 240p for a short time. The supplied gas substantially is not thus decomposed. The film formation rate is decreased and the material gas is not effectively used. For this reason, the mixture gas of the material gas for film formation and the He gas is supplied into the discharge space at a Q/S of 1 secxe2x88x921 to 102 secxe2x88x921 so that the gas in the whole discharge space is replaced in 10xe2x88x922 sec to 1 sec.
The above-described conventional technology has the following problems.
The film formation chamber 241 is filled with the mixture gas of the material gas for film formation and the He gas so that the pressure inside the chamber 241 is around the atmospheric pressure. The high-pressure plasma 240p is generated under such a high-pressure atmosphere. The plasma 240p decomposes the material gas for film formation. The decomposed material forms a film on the sample substrate 245. Because the film formation chamber 241 is filled with the mixture gas around the atmospheric pressure, reaction products generated in the plasma 240p are diffused outside the plasma 240p before being floated for a long time and condensed in the atmosphere. For this reason, the grain diameter of the reaction product as well as the number of such a reaction product is thus increased. The reaction product having the increased grain diameter is attached onto the surface of the sample substrate 245. The contamination of the grain-like product leads to a decrease in quality of a film. The reaction product is also attached onto the inner wall of the film formation chamber 241, thereby reducing the yield of this process.
Further, since the film formation chamber is filled with the high-pressure gas around atmospheric pressure, the number of moles of gas leaking outside the film formation chamber is large once the gas leak occurs. The safety of the apparatus is thus low.
Furthermore, it takes a long time to purge the reaction gas out of the film formation chamber 241 when removing the sample substrate 245. For this reason, although the film formation rate is fast, the throughput of the whole process of the apparatus is low.
The above-described three problems are ascribable to the whole reaction container being filled with high-pressure atmosphere.
Moreover, when the gap 240g between the electrodes is small, a reaction gas flow blowing off from the holes of the porous plate high resistor 244 collides with a surface of the sample substrate 245. A portion of the sample substrate 245 immediately under the blowoff hole has a film formation distribution different from the peripheral portion surrounding the hole. This leads to a reduction in uniformity of a film on the sample substrate 245.
When the gap 240g between the electrodes is small, the tilt of the non-ground electrode 242 with respect to the sample substrate 245 leads to a change in the flow amount distribution of the reaction gas, thereby reducing the uniformity of a film.
A power load is applied to the non-ground electrode 242. The sample substrate 245 is provided on the ground electrode 243. Since the high-pressure plasma 240p, which is difficult to be diffused, is generated between the non-ground electrode 242 and the ground electrode 243, the high-pressure plasma 240p is difficult to be generated on the entire sample substrate 245. It is thus difficult to obtain a uniform film on the entire sample substrate having a large area. Alternatively, the plasma 240p is generated on a portion of the sample substrate 245 which is smaller than the whole sample substrate 245. The non-ground electrode 242 and the sample substrate 245 are relatively moved in such a way as to form a film on the entire sample substrate 245. In this case, the movement of the electrode 242 or the substrate 245 changes the equivalent circuit of a power supply path, resulting in a film formation amount distribution. The uniformity of a film is thus reduced.
Among the above-described conventional problems, a description will be given of the first problem described above in connection with the formation and attachment of the reaction product having a large grain diameter, and the fourth problem described above in that the film formation amount distribution changes at a portion immediately under the blowoff holes of the porous plate high resistor 244.
Initially, a description will be given of principles of degradation of the quality of a film and a decrease in process yield due to filling the inside of the film formation chamber 241 with gas around atmospheric pressure.
The supplied material gas is decomposed in the atmospheric-pressure plasma 240p before reaching the sample substrate 245 to form a film on the sample substrate 245. In the plasma 240p, in addition to the decomposition and dissociation of the material gas, polymerization and condensation reactions occur at the same time. For this reason, there are a number of powder-like reaction products made of impurities contaminating the inside of the film formation chamber 241 and the material gas atoms. These reaction products also reach a surface of the substrate 245. The reaction products which are condensed in the plasma are immediately decomposed by the plasma 240p. The condensed reaction products do not contaminate the film formed on the substrate 245. The reaction product which is discharged outside the plasma 240p is not decomposed but are condensed with each other or impurities in the reaction container, increasing the grain diameter thereof. The number of the reaction products having such a large grain diameter is also increased. It is the reaction product having a large grain diameter that causes a problem. Such are action product is not easily decomposed when it is diffused into the plasma 240p. The reaction product having a large grain diameter can thus reach the sample substrate 245 and contaminates the film formed on the substrate 245, thereby reducing the quality of the film significantly. Further, the reaction product having a large grain diameter is attached onto the inner wall of the film formation chamber 241 and contaminates the inside of the film formation chamber 241, resulting in contamination of the film surface after the film formation. This decreases the process yield.
There is a problem in that in the above-descrlbed conventional technology, the outside of the plasma 240p has the same level of pressure as that of the inside of the plasma 240p so as to fill the inside of the film formation chamber 241 with gas having a high pressure around atmospheric pressure. A plausible way to solve the problem is to reduce the pressure of the atmosphere in the film formation chamber 241 so as to prevent an increase in the grain diameter and the number of grains of the reaction products outside the plasma 240p. In this case, however, the pressure of the plasma 240p also is decreased, so that the film formation rate is lowered and the throughput of the process is reduced.
As described above, in the conventional technology, the film formation under around atmospheric pressure leads to a decrease in film quality. Alternatively, the film formation under a lowered pressure does not allow the fast-rate film formation. These problems are ascribable to the conventional method in which the film formation is performed by generating the plasma 240p in the film formation chamber 241 which is filled with gas having the same level of pressure as that of the plasma.
Next, a description will be given of the film thickness distribution generated when film formation is performed immediately under a supply inlet of the porous plate high resistor 244 with reference to FIG. 25.
FIG. 25 is a diagram illustrating a film thickness distribution of a thin film 252 formed immediately under a reaction gas supply inlet 250. In FIG. 25, referencenumeral 250 indicates the gas supply inlet; 251 the floe of reaction gas colliding with the a sample substrate: 252 a thin film formed on the substrate; and 253 a protrusion portion of the thin film 252 formed immediately under the reaction gas supply inlet 250.
In the conventional structure shown in FIG. 24, the plasma 240p having a pressure around atmospheric pressure is generated between the non-ground electrode 242 and the sample substrate 245. A mixture gas of He gas and a material gas is blown into the plasma region from a number of the gas supply inlets 250. For example, a gap between the electrodes 242 and 243 is 0.1 mm to 10 mm in the above-described publication.
However, when the gap between the electrodes 242 and 243 is small, a flow 251 of the reaction gas blown off from the gas supply inlet 250 collides perpendicularly with a surface of the sample substrate immediately under the gas supply inlet 250. The portion immediately under the inlet 250 is efficiently supplied with the reaction gas, resulting in a larger film formation amount than the peripheral portion. Therefore, a protrusion portion (uneven film thickness distribution) 253 is formed as shown in FIG. 25.
In the conventional technology shown in FIG. 24, the gap between the electrode 242 and the sample substrate 245 cannot be lessened so as to prevent the This problem is ascribable to the structure in which the plasma 240p is generated between the electrode 242 and the sample substrate 245 and the reaction gas supply inlet 250 is provided at the plasma generating portion.
In the above description. the problems are explained when a film is formed on the sample substrate 245 using the conventional technique. Similar problems arise when the surface modification is performed.
According to one aspect of the present invention, a method for treating a surface of a sample using plasma includes the steps of placing the sample in a predetermined atmosphere; locally supplying a reaction gas from a reaction gas supply portion to a vicinity of the sample; providing a wall surface opposed to the sample; providing a gas flow path having a low conductance from the reaction gas supply portion to the atmosphere; and locally forming a high-pressure reaction gas region having a pressure higher than the atmosphere in the gas flow path having a low conductance; and generating locally high-pressure plasma based on the reaction gas in the high-pressure reaction gas region: and subjecting the sample to surface treatment using an active seed in the high-pressure plasma.
In one embodiment of this invention, the atmosphere is provided in a reaction container comprising an electrode having a shape corresponding to a surface shape of the sample. The sample is separately provided in the atmosphere, or on a sample stage having a shape corresponding to the surface shape of the sample and provided in the reaction container. The reaction gas supply portion is provided at least one of the electrode and the sample stage.
According to another aspect of the present invention, an apparatus for treating a surface of a sample using plasma, wherein the sample is provided in a predetermined atmosphere: a reaction gas from a reaction gas supply portion is supplied to a vicinity of the sample locally: a wall surface is provided opposed to the sample; a gas flow path having a low conductance is provided from the reaction gas supply portion to the atmosphere: and a high-pressure reaction gas region havi ng a pressure higher than the atmosphere is locally formed in the gas flow path having a low conductance; and high-pressure plasma based on the reaction gas is generated in the high-pressure reaction gas region locally; and the sample is subjected to surface treatment using an active seed in the high-pressure plasma.
In one embodiment of this invention, the apparatus further includes a section for providing px/p0 greater than 1 where the px/p0 is a ratio of a pressure px of a region in which the high-pressure plasma is generated locally in the high-pressure reaction gas region to a pressure p0 of the atmosphere.
In one embodiment of this invention, the apparatus further includes a section for providing locally the high-pressure plasma at a position away from the reaction gas supply portion in the high-pressure reaction gas region.
In one embodiment of this invention, the apparatus further includes a sample stage, wherein the sample is placed on the sample stage; and the sample stage has a shape corresponding to the sample.
In one embodiment of this invention, the apparatus further includes a power supply and an electrode, wherein the wall surface is provided by using the surface of the electrode; power is applied to the electrode to generate the high-pressure plasma.
In one embodiment of this invention, the electrode has a shape corresponding to the shape of the sample.
In one embodiment of this invention, the electrode further has a reaction gas supply inlet for supplying the reaction gas to the gas flow path having a low conductance.
In one embodiment of this invention, the electrode is opposed to the sample; there is a micro gap between the electrode and the sample: a surface opposed to the sample of the electrode functions as the wall surface.
In one embodiment of this invention, at least one of the electrode and the sample stage is movable. Due to a difference in pressure between a pressure of the atmosphere in the reaction container and a pressure of the reaction gas supplied from the reaction gas supply portion, one of the electrode and the sample stage is floated with respect to the other; there is a micro gap between the electrode and the sample; and a surface opposed to the sample of the electrode functions as the wall surface.
In one embodiment of this invention, at least one of the electrode and the sample stage is movable. An arrangement for generating a magnetic force having a predetermined magnetic intensity is provided on at least one of the electrode and the sample stage. Due to the magnetic force generated by the arrangement, one of the electrode and the sample stage is floated with respect to the other; there is a micro gap between the electrode and the sample; and a surface opposed to the sample of the electrode functions as the wall surface.
In one embodiment of this invention, at least one of the electrode and the sample stage is movable. An arrangement for generating a magnetic force having a predetermined magnetic intensity is provided on at least one of the electrode and the sample stage. Due to the magnetic force generated by the arrangement and a difference in pressure between a pressure of the atmosphere in the reaction container and a pressure of the reaction gas supplied from the reaction gas supply portion, one of the electrode and the sample stage is floated with respect to the other: there is a micro gap between the electrode and the sample; and a surface opposed to the sample of the electrode functions as the wall surface.
In one embodiment of this invention, a power transmission line is provided in the electrode. The power transmission line has an open end at a predetermined position of a portion opposed to the sample of the electrode. The power transmission line in the electrode transmits power applied to the electrode to the open end: a high electric field is generated at the open end by the transmitted power. The high-pressure plasma is generated in a vicinity of the open end by the high electric field.
In one embodiment of this invention, the power transmission line in the electrode includes an inner conductor for applying the power and an electric field shielding conductor which covers the inner conductor via an insulator and is connected to ground.
In one embodiment of this invention, the power app lied to the electrode is radio-frequency power having a frequency band of about 10 MHz to about 1 GHz, or microwave power having a frequency band of about 1 GHz or greater.
In one embodiment of this invention, the power transmission line comprises a waveguide which is provided in the electrode and has an open end at a predetermined position of a portion opposed to the sample of the electrode.
In one embodiment of this invention, the apparatus further includes a power absorber having a large absorption coefficient with respect to an electromagnetic wave having a frequency of a power supply used. The power absorber is provided in at least one of the electrode and the sample stage. The power absorber is provided at a region in the gas flow path having a low conductance having a pressure lower than the high-pressure plasma generated region. The power absorber absorbs an electromagnetic wave passing through the high-pressure plasma generated region to prevent plasma generation in the atmosphere in a region surrounding the high-pressure plasma.
In one embodiment of this invention, the apparatus further includes a discharging outlet having an opening which is directed to the micro gap between the electrode and the sample. The discharging outlet is provided in at least one of the sample stage or the electrode. A reaction product generated in the high-pressure plasma is discharged from the discharging outlet.
In one embodiment of this invention, a portion of a surface opposed to the sample of the electrode has a shape similar to a surface of the sample. The high-pressure plasma is generated in a flow along the surface of the sample from a high-pressure region in a vicinity of the reaction gas supply portion to the atmosphere around the electrode or to the discharging outlet.
In one embodiment of this invention, the apparatus according to claim 3 further includes a reaction container for maiintaining the predetermined atmosphere.
In one embodiment of this invention, the apparatus further includes a reaction container for maintaining the predetermined atmosphere; and a section for reprocessing a gas discharged from the reaction container or the discharging outlet and supplying the gas into the reaction container or the reaction gas supply portion again as the reaction gas or the atmosphere.
In one embodiment of this invention, the apparatus further includes a section for providing a relative movement between the sample and the high-pressure plasma so that the entire sample is subjected to surface treatment.
Thus, the invention described herein. makes possible the advantages of providing (1) a surface treatment method and apparatus using plasma in which film formation or surface modification is efficiently performed on a surface of a sample, and in clean atmosphere, film formation or surface modification is satisfactorily performed on a surface of a sample without attaching inappropriate reaction products onto the sample surface; and (2) a surface treatment method and apparatus using plasma in which the desired pressure of an atmosphere gas is lower than that of a plasma generating portion or is held under vacuum, so that film formation or surface. modification is uniformly performed on a sample having a large area without generating condensation of reaction products and without generating an uneven distribution of a film formation amount or treated layer thickness immediately under the reaction gas blowoff region.